The present invention relates to the use of silica staple fibers which are prepared from dry-spun soda water glass fibers by treating the dry-spun soda water glass fibers with acid and/or salt solutions which contain hydrogen ions, which are to be used in the production of mineral insulated conductors.
Mineral insulated conductors have existed for a long time. Mineral insulated conductors are defined to be conductors or cables containing one or more metallic conductors, preferably. For example, copper wires embedded in an inorganic mass prepared from an inorganic powder. The embedded conductors, including their inorganic insulation, are covered by a metallic envelope, the so-called sheathing.
Mineral insulated conductors of the type described above are discussed in an article by E. Mill entitled "Mineral Insulated Metal Sheathed Cables" in Wire Industry, May 1976, pages 409 to 413. The insulation of the metallic cores in the mineral insulated conductor by an inorganic powder has many disadvantages including high conductor capacitance. This essentially is due to the high dielectric constant of the powder insulation used.
DE P No. 103479 describes heating conductors surrounded by a metal sheathing, said conductors being electrically insulated from said sheathing by glass fibers. The above cited patent further discloses that glass fibers leached with hydrochloric acid may also be used, so that these fibers will primarily consist of pure silica.
Glass fibers, however, have inadequate insulating capability, while leached glass fibers are very brittle and are difficult to process.
This invention was developed in view of the foregoing background and to overcome the foregoing drawbacks.